I've thought about this before, because as lyrics go, I find this to be one of Regina's most intriguing songs. I sort of agree with both of you: I think it's about being vulnerable -- "open" -- and the potential for both pain and pleasure humans have (how "perpetually human" of us). There is hope in the idea that life and people are always "potentially lovely", but at the same time, the gasping, "in a room I've built myself" part of the song does speak of loneliness and depression to me, and that is, after all, another part of the human experience.
Or maybe the song is about the difference between allowing yourself to feel vulnerable and open -- and the feeling of freedom and suspension in that state of being -- and building walls around yourself and thereby feeling trapped instead.